The present invention generally relates to spacers for a nuclear fuel bundle and particularly relates to an adjustment tool and method of using the tool for adjusting the spring force of the spacer springs.
Nuclear fuel rod spacers for nuclear fuel rod assemblies are typically designed with spring mechanisms in the spacers that exert preload forces normal to each fuel rod in each fuel rod cell of the spacer. By preload forces is meant the forces applied in initially manufactured spacers before irradiation or other activities that would potentially stress the springs and result in a reduction of the spring forces. Typically, these preload forces are specified in the range of about one to three pounds for each spacer cell. A spring force outside of the specified range is grounds for rejection of the entire spacer. A known device, for example, see U.S. Pat. No. 5,215,705, can measure the spring force of the spacer spring. However, the device disclosed in that patent does not adjust the spring force of the spacer spring. Accordingly, there is a need for a tool for adjusting the spring force of spacer springs after initial manufacture of the spacer should the spring preload forces lie outside a predetermined range of preload forces.
In accordance with a preferred embodiment of the present invention, there are provided a pair of adjustment tools for making calibrated adjustments in the spacer spring dimensions thereby to alter the spring forces in fabricated spacer assemblies. It is necessary to make adjustment to the spring forces in fabricated spacers in a manner that can be both calibrated and will not result in unacceptable damage to the spacers. Such tools must also meet standard requirements for nuclear fuel manufacturing including fabrication of the tools from nuclear grade materials and tools which will not damage the spacers or springs during insertion or removal nor contaminate the spacer with foreign materials or debris. Two distinct tools are provided for respectively displacing the spacer spring in an outward or an inward direction, depending upon the measured spring force. For displacing the spring in an outward direction to adjust the spring force, the tool includes a holder having a head, a probe depending from the head for insertion into the spacer opening and a lever pivoted to the holder. A micrometer is preferably secured to the head and has a displaceable drive head for engaging one end of the pivoted arm. By displacing the one end of the pivoted arm, the opposite end engages the spring and displaces the spring outwardly relative to the probe and spacer opening to adjust, i.e., decrease, the spring force.
Where the spring requires displacement inwardly toward the opening, the second tool includes a holder having a probe, a depending pivotal arm laterally outwardly of the probe and a micrometer attached to the head. The probe and pivotal arm are located in the spacer to straddle the spring. By displacing the drive head of the micrometer in engagement with one end of the pivoted arm, the opposite end of the pivoted arm engages the spring to displace the spring inwardly toward the probe thereby adjusting, i.e., increasing the spring force of the spacer spring in the cell receiving the probe. In both tools, the change in spring force is established by calibrating the micrometer setting against a resulting spring force for springs in test or calibration spacers, e.g., as measured by a spring force measurement tool such as described in the aforementioned U.S. Pat. No. 5,215,705. There is a linear relationship where the deformation constant is determined from empirical data collected by measuring the spring force before and after bending the spring with the tool hereof to various recorded set points. Once this constant has been determined the amount of deflection needed to alter the spring force to any given value can be readily determined using this equation. The deformation constant is given by the equation: xcex94 Spring Force=(Deformation Constant)(xcex94 Spring Deflection).
In a preferred embodiment according to the present invention, there is provided apparatus for adjusting the spring force of springs of a spacer for a nuclear fuel bundle, comprising a tool including a tool holder probe for insertion into the opening of a spacer and a movable drive head and an arm carried by the tool and pivoted intermediate opposite ends thereof, the arm extending generally parallel to the probe and having a drive head engaging surface for pivoting the arm in response to movement of the tool drive head and a spacer spring engaging surface adjacent an opposite end thereof for displacing the spring thereby adjusting the spring force of the spring.
In a further preferred embodiment according to the present invention, there is provided a method of adjusting the spring force of a spring in a spacer cell opening of a spacer for a nuclear fuel bundle, comprising the steps of providing a holder having a probe and a displaceable arm, inserting the probe into the spacer opening and displacing the arm to displace the spring to thereby adjust the spring force of the spacer spring.